<?php 
header("Content-Type: text/html; charset=UTF-8");
$array = array(
    '0'=>array(
        '零分测试内容1',
        '零分测试内容2',
        '零分测试内容3',
    ),
    '20'=>array(
        '20分测试内容1',
        '20分测试内容2',
        '20分测试内容3',
    ),
    '45'=>array(
        '45分测试内容1',
        '45分测试内容2',
    ),
    '60'=>array(
        '60分测试内容1',
        '60分测试内容2',
        '60分测试内容3',
        '60分测试内容4',
    ),
);

$score = 59;
foreach($array as $key => $value){
    if($key>$score){
        continue;
    }
    $scoreArray = $value;
}
$count = count($scoreArray);
echo $scoreArray[rand(0,$count-1)];